Re: [PATCH] xen: add kconfig for event_fifo

[Jan Beulich <jbeulich@xxxxxxxx>]

On 21.03.2025 22:30, Stefano Stabellini wrote:
> On Thu, 20 Mar 2025, Jan Beulich wrote:
>> On 19.03.2025 00:40, Stefano Stabellini wrote:
>>> Evtchn fifos are not needed on smaller systems; the older interface is
>>> lightweight and sufficient. Make it possible to disable evtchn fifo.
>>>
>>> Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxx>
>>
>> Let me ask a more general question, before considering whether to ack:
>> When kconfig was introduced into Xen, the expectation was (iirc) that
>> we wouldn't grow its use to the fine grained granularity that it has
>> been having in Linux. The more build-time controls we have, the harder
>> it is to know whether a certain piece of code was actually included in
>> a build someone, say, reports a problem with. Are we knowingly moving
>> away from that earlier position? evtchn_fifo.c isn't actually that
>> much code to exclude, after all ...
> 
> 
> I think we need to be more flexible with build-time controls. The extent
> to which we should be flexible is an interesting discussion to have.
> 
> However, this patch is not for code size. This code causes unnecessary
> runtime anonymous memory allocations, which are highly undesirable. In
> fact, it is the primary source of such allocations. Additionally, it
> exposes an extra interface to the guest, which is also undesirable
> unless necessary.
> 
> In other words, the issue is not the size of the code, but its impact.

This may help if it was said in the description.

Jan